The long-term goal of this research program is to determine the factors that influence how children learn the words of the language and use this evidence to develop a comprehensive model of word learning across normal and impaired language development. Ultimately, this model will be used to construct clinical diagnostic and treatment techniques to improve word learning, minimizing future deficits in language acquisition. Across planned projects, we examine similarities and differences in the contribution of representations of sounds (i.e., phonological representations), whole-word forms (i.e., lexical representations), and meaning (i.e., semantic representations) to both simple associative learning (i.e., initial mapping) and long-term integrative learning (i.e., extended mapping). Four projects are planned with multiple studies in each project to independently address sound, whole-word froms, and meaning. At the macroscopic level, Project A focuses on developmental changes in word learning from preschool to adulthood, and Project B explores word learning differences between children with normal language and those with specific language impairment. At the microscopic level, Project C examines whether incremental changes in representations produce corresponding incremental changes in word learning. Project D explores whether specific types of relationships between novel and known representations influence learning of new representations. Projects C and D also investigate whether properties of sounds, whole-word forms, and/or meaning can be manipulated during exposure to enhance word learning. The resulting findings will provide the necessary evidence to build a comprehensive model of the learning of sound, word-form, and meaning representations that can be used to develop theoretically motivated clinical techniques. The health benefit of this research is that many children with language impairments have difficulty learning new words, yet the cause of this deficit is poorly understood. Early word learning is critical because it may set the foundation for acquisition of reading decoding, reading comprehension, and academic success. Children who enter elementary school with vocabulary deficits have difficulty closing the gap with their peers. Thus, effective word learning instruction is critical in preventing reading and academic failure. Theoretically motivated diagnostic and treatment methods may minimize this risk.